摘要:

A reanalysis of the Pioneer Venus electron temperature data base showed a strong correlation between elevated electron temperatures and induced magnetic fields in the day side ionosphere above about 200 km. These results suggest, although not conclusively, that the elevated temperatures are the result of reduced vertical conductivities caused by the horizontal, induced fields with a possible contribution from energy deposition by magnetosheath electrons moving along the field from the tail region.

ISSN:0094-8276    

DOI:10.1029/93GL01452

年代:1993

数据来源: WILEY

摘要:

We have made a detailed analysis of several periods of the AE time series and find that the average correlation dimension is 3.4. We have generated bicolored noise and shown that it shares many properties with the AE data. We also find that the AE time series is self‐affine such that the affinity exponent changes on a time scale of about two hours, which is a typical length of magnetospheric substorms. We suggest that this same time scale appears as a spectral break at about 5.6 × 10−5Hz (5‐hour period) in the power spectrum of the A

ISSN:0094-8276    

DOI:10.1029/93GL01596

年代:1993

数据来源: WILEY

摘要:

A simple model using random walk jumps in velocity space whose path lengths are governed by a power law or Lévy flight probability distribution is shown to generate distribution functions that are Maxwellian at low velocities and power law at high velocities

ISSN:0094-8276    

DOI:10.1029/93GL01702

年代:1993

数据来源: WILEY

摘要:

Examination of Viking UV images of the morning auroral oval at times of high activity has shown three distinct types of auroral feature. Moving spots at the equatorward border of the oval are found to be associated with Ps 6 magnetic disturbances observed from the ground. Discrete, periodically spaced, features at high latitude are also observed. A variable but stationary emission feature is seen near the dawn terminator. The discrete features are manifestations of the Kelvin‐Helmholtz instability (KHI) on shear layers created by high speed flow between them, based on quantitative estimates of phase velocity, wave number, and growth rate. The terminator feature may arise from precipitating electrons forming the upward electrical current in part of the large‐scale driven system. This part of the driven system is caused by the conductivity gradient at dawn and has been previously detected by other me

ISSN:0094-8276    

DOI:10.1029/93GL01594

年代:1993

数据来源: WILEY

摘要:

A Boltzmann formulation of the electron distribution function and Maxwell's equations for the electromagnetic (EM) fields are used to simulate the interaction of lightning radiated EM pulses with the lower ionosphere. Ionization and dissociative attachment induced by the heated electrons cause significant changes in the local electron density (Ne). Due to ‘slow’ field changes of typical lightning EM pulses over time scales of tens of µs, the distribution function follows the quasi‐equilibrium solution of the Boltzmann equation in the altitude range of interest (70 to 100 km). The EM pulse is simulated as a planar 100 µs long single period oscillation of a 10 kHz wave injected at 70 km. Under nighttime conditions, individual pulses of intensity 10–20 V/m (normalized to 100 km horizontal distance) produce changes in Neof 1–30% while a sequence of pulses leads to strong modification of Neat altitudes<95 km. The Nechanges produce a ‘sharpening’ of the lower ionospheric boundary by causing a reduction in electron density at 75–85 km (due to attachment) and a substantial increase at 85–95 km (due to ionization) (e.g., the scale height decreases by a factor of ∼2 at ∼85 km for a single 20 V/m EM pulse). No substantial Nechang

ISSN:0094-8276    

DOI:10.1029/93GL01696

年代:1993

数据来源: WILEY

摘要:

A growing body of evidence based on radar and optical observations of winds in the Earth's upper atmosphere indicates that the commonly utilized value for the ion‐neutral atomic oxygen (O+‐O) collision frequency for momentum transfer is too low by a factor of 1.3–2. A revised standard for the O+‐O momentum transfer collision frequency is therefore recommended based on all the available measurements, in order to facilitate comparisons with thermospheric and ionospheric models and among data sets until future accurate laboratory measurements and more reliable observations can be made. The new interim standard, representing a 70% increase from the previous value, is given by: ν o+−o = 4×10−17Tr0.5no, where Tr= (Ti+Tn)/2, Tibeing ion temperature, Tnneutral temperature, and noatomic oxygen number d

ISSN:0094-8276    

DOI:10.1029/93GL01699

年代:1993

数据来源: WILEY

摘要:

The structure of short period (2–4 days) planetary waves in the Antarctic mesosphere has been determined from ground based wind measurements. At the South Pole observations are made with a Fabry‐Perot spectrometer (FPS) to determine the meridional wind component of OH tracer molecules. Azimuth scanning of the FPS shows that the observed modes are of zonal wavenumber one, as expected at the rotation pole in the neutral atmosphere. At Scott Base (78°S) observations are made with an MF spaced‐antenna mode mesospheric wind‐profiler radar. The vertical structure of the waves at altitudes of 80–100 km shows a phase variation corresponding to a vertical wavelength of more than 100 km. The observed periods support previous interpretations, based on satellite observations and barotropic instability models, of modes associated with the

ISSN:0094-8276    

DOI:10.1029/93GL01707

年代:1993

数据来源: WILEY

摘要:

Limb sounding of mesospheric water vapor using pure rotational emission in the long‐wavelength infrared region has been demonstrated using data from the ELC‐1 rocket experiment, launched in October, 1983. By simultaneously analyzing H2O emission at 23–29 µm and CO2emission in the ν2band region, effects due to uncertainties in the atmospheric temperature and instrument calibration are minimized. The H2O profile obtained from ELC‐1 is consistent with other fall to early‐winter measurements. Given accurate line‐of‐sight pointing information, this approach will be feasible for global mesospheric H2O sounding from limb‐v

ISSN:0094-8276    

DOI:10.1029/93GL01403

年代:1993

数据来源: WILEY

摘要:

Ozonesonde measurements at Hilo, Hawaii (20°N), after the eruption of Pinatubo in June 1991, are compared to measurements made there from 1985 to 1990 in order to investigate possible volcanic effects. The general nature of the ozone anomalies in 1991–92 can be summarized as lower than normal ozone below about 25 km and higher than normal ozone above. The net result was that total ozone was somewhat lower than average and, during late 1992, was as low as recorded in 1982, following the eruption of El Chichón. Elevated temperatures in the region of the volcanic aerosol layer and upward motion of the aerosol layer were observed at Hilo following the eruption. Although the nature of the perturbed ozone profile may be the result of enhanced upward motion associated with volcanic aerosol particle heating, and the coupling of quasi‐biennial oscillation effects, the persistent nature of the perturbation, still present more than a year after the eruption, is not easily expl

ISSN:0094-8276    

DOI:10.1029/93GL01585

年代:1993

数据来源: WILEY

摘要:

The relation between depth of the Antarctic ozone hole, and equatorial QBO and SST, is reexamined for the interval 1962–1992, using Dobson total‐ozone data at the South Pole, Singapore 50 mb zonal wind, and average SST in the El Nino region 12S–2N, 180–90W. During this interval the correlation between October–November values of South Pole total ozone, and south polar 100 mb temperature from radiosondes, is 0.93. In 23 of 27 cases, South Pole springtime (October–November) total ozone decreased from one year to the next when the Singapore 50 mb zonal wind averaged from the east during the intervening 3 seasons and increased when this wind averaged from the west. Owing to the high serial correlation of the wind and total‐ozone data, this distribution is only significant at the 5% level according to the Chi‐square test, but basically supports the conclusions of Garcia and Solomon (1987) and Lait et al. (1989) regarding the relation between equatorial QBO and depth of the ozone hole. The tendency for a deeper ozone hole when equatorial SST warms (El Nino) yields a relation between depth of the Antarctic ozone hole, and equatorial QBO and SST, significant at the 1% level only by the subjective drawing of a smooth line which separates springtime total‐ozone increases and decreases from one year to the next in 24 of 25 cases with 2 cases on the line of separation. The Singapore 50 mb wind has been from the west during the first half of 1993, suggesting a less deep ozone hole in 1993 than in 1992, especially if the current prolonged El Nino finally a

ISSN:0094-8276    

DOI:10.1029/93GL01762

年代:1993

数据来源: WILEY